High purity composite useful as furnace components

ABSTRACT

A Czochralski process furnace component is disclosed. The component comprises a high purity, semiconductor standard composite including a carbon fiber reinforced carbon matrix having a level of metal impurity below the detection limit of inductively coupled plasma spectroscopy. A process for producing the components includes heat treatment of the carbon fiber and the components.

This is a divisional of application Ser. No. 08/394,605filed on Feb. 27,1995now U.S. Pat. No. 5,683,281.

TECHNICAL FIELD

The present invention is directed to high purity composites of carbonfiber within a carbon matrix and their preparation. More particularly,the present invention is directed to high purity composites useful assemiconductor material processing components, such as Czochralskifurnace components and furniture.

BACKGROUND OF THE INVENTION

Silicon wafers for use in the semiconductor industry are produced by avariety of methods. One of the methods is that referred to as theCzochralski or "CZ" technique. In the CZ technique a seed crystal ofknown orientation is immersed in a molten pool of silicon. This triggerssolidification and precipitation of the silicon. As the crystal ismechanically pulled upwardly from the pool, the orientation of thesolidifying front mimics that of the seed crystal. Silicon wafers can bemanufactured from the solid ingot by machining and polishing.

Specifically constructed furnaces are used to accurately control thevarious parameters needed to ensure that high quality crystals areproduced. Several of the key components in CZ crystal growing furnacesare made from graphite. These include various liners, shields, tubes,crucible susceptors and the like. Graphite has been the materialconventionally utilized in such processes due to its high temperaturecapability and relative chemical inertness.

Disadvantages of graphite include its poor durability brought about byits highly brittle nature and its tendency to microcrack when exposed torepeated temperature cycles. Such microcracking alters the thermalconductivity of the component which in turn makes accurate temperaturecontrol of the silicon melt difficult. In addition, contamination of thesilicon melt may occur by the leaching of impurities from the graphitecomponents or from particulates generated by the degradation of thegraphite itself. Semiconductor standards require extremely low levels ofimpurities in the semiconductor processing system, to allowsubstantially no impurities to be incorporated into the semiconductormaterial, as even trace amounts can alter the electronic properties ofthe semiconductor material.

Further, the deposition of oxides of silicon on graphite parts duringthe production of the silicon crystal occurs to such an extent thatparts must be cleaned on a regular basis and replaced periodically.Replacing worn graphite parts is a time consuming and costly process.

Therefore, there has been a need for the manufacture of components forCZ crystal growing reactors that have the advantages of graphite withoutthe disadvantages. Such components would enable the more cost effectiveproduction of high quality silicon semiconductor wafers.

There have been attempts made to utilize carbon/carbon composites insimilar electronic material production processes, in place of graphitefurnace components and furniture. U.S. Pat. No. 5,132,145 andcorresponding European Patent application 88401031.5 to Valentiandisclose a method of making a composite material crucible for use in theBridgman method for producing single crystals of metallic materialsemiconductors.

Valentian proposed making a cylindrical crucible for holding a moltensample, from a single wall of carbon fibers or silicon carbide fibersimpregnated with carbon or silicon carbide, and depositing on the innerwall of the crucible, a thin inner lining of silicon carbide incombination with silica, silicon nitride, and silicon nitride/alumina,or in other embodiments, amorphous carbon, boron nitride, titaniumnitride or diboride, and zirconium nitride or diboride. The thin innerlining is required to avoid contamination of the molten sample, toprovide a matched thermal conductivity with the molten sample, and toavoid crack propagation which is a drawback of the bulk material.

It is therefore an object of the present invention to provide componentsfor use in semiconductor processing that are superior in mechanical andthermal properties to conventional graphite components.

It is a further object of the present invention to provide componentsfor use in semiconductor processing that are superior in puritycharacteristics to conventional graphite components and to conventionalcarbon/carbon materials.

SUMMARY OF THE INVENTION

The present invention provides a high purity carbon/carbon compositematerial consisting of carbon fiber reinforcements within a carbonmatrix. This material has outstanding thermal capabilities, especiallyin non-oxidizing atmospheres. Before the present invention, use ofcarbon/carbon composite materials in the electronics industry waslargely restricted due to the inability to produce materials that notonly exhibit good mechanical properties at high temperature but that areextremely pure and will not contaminate sensitive electronic productionarticles such as semiconductor materials or devices, and silicon wafersin particular.

The present invention therefore provides a high purity, semiconductorstandard composite comprising a carbon fiber reinforced carbon matrixhaving a level of metal impurity below the detection limit ofinductively coupled plasma spectroscopy for the metals Ag, Al, Ba, Be,Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn.

The present invention further provides semiconductor processing, such asCzochralski crystal growing, furnace components and furniture comprisingthe above high purity, carbon/carbon composite, the composite includinga carbon fiber reinforced carbon matrix having a level of metal impuritybelow the detection limit of inductively coupled plasma spectroscopy forthe metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P,Pb, Sr and Zn. In one embodiment, the present invention provides asemiconductor processing furnace heat shield or furnace tube linercomprising the high purity, semiconductor standard composite. In anotherembodiment, the present invention provides a Czochralski processcrucible susceptor comprising the high purity, semiconductor standardcomposite.

The present invention also provides a semiconductor crystal growingapparatus comprising at least one high purity, carbon/carbon compositecomponents, said composite including a carbon fiber reinforced carbonmatrix having a level of metal impurity below the detection limit ofinductively coupled plasma spectroscopy for the metals Ag, Al, Ba, Be,Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn.

According to the present invention, therefore, there is provided aCzochralski crystal growing process for pulling a semiconductor ingotfrom a semiconductor material melt, such as a silicon ingot from asilicon melt, including providing the semiconductor material (such assilicon) melt in a quartz crucible, wherein the quartz crucible isisolated from contaminant sources by at least one high purity,carbon/carbon composite component. In one embodiment, the processincludes intimately supporting the crucible with the above susceptor. Inanother embodiment, the process includes disposing the furnace heatshield or furnace tube liner between the crystal pulling zone and theheating element.

The present invention also provides a process for the production of ahigh purity, semiconductor standard carbon/carbon composite comprising:

heating a carbon fiber reinforcement to at least about 2400° C.,

impregnating the carbon fiber with a matrix precursor of high purity(semiconductor quality) carbon,

carbonizing the impregnated fabric to form a carbonized part,

densifying the carbonized part with high purity carbon to form acomponent, and

heating the component at a temperature of at least about 2400° C. toform a heat treated component, and

heating the heat treated component at a temperature of at least about2400° C. in a halogen atmosphere to form the high purity composite.

In one embodiment, densifying the carbonized part includes purging a CVDprocessing furnace with an inert gas at a temperature of at least about2400° C., and densifying the carbonized part with CVD carbon in thepurged CVD furnace to form the component.

I have therefore found that it is possible to produce carbon/carbonmaterials with the desired mechanical, thermal, chemical and physicalcharacteristics that make these materials very suitable for use in thesemiconductor electronics industry, and particularly for use assemiconductor processing furnace, such as crystal growing reactor,furniture and components

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 1A are a schematic cross sectional views of semiconductorprocessing furnaces, specifically Czochralski crystal growing reactors.

FIG. 2 is a perspective view of a furnace heat shield, or furnace tubeliner.

FIG. 3 is a plan view of a furnace heat shield, or furnace tube liner.

FIG. 4 is an elevational view of a furnace heat shield, or furnace tubeliner.

FIG. 5 is a plan view of a high purity composite crucible susceptor.

FIG. 6 is an elevational view of a high purity composite cruciblesusceptor.

FIG. 7 is a perspective view of a high purity composite cruciblesusceptor.

FIG. 8 is a plan view of an alternate high purity composite cruciblesusceptor.

FIG. 9 is an elevational view of an alternate high purity compositecrucible susceptor.

FIG. 10 is a perspective view of an alternate high purity compositecrucible susceptor.

DETAILED DESCRIPTION OF THE INVENTION

Carbon fiber reinforced carbon matrix materials, or carbon/carboncomposites, have thermal stability, high resistance to thermal shock dueto high thermal conductivity and low thermal expansion behavior (thatis, thermal expansion coefficient or TEC), and have high toughness,strength and stiffness in high-temperature applications. Carbon/carboncomposites comprise carbon reinforcements mixed or contacted with matrixprecursors to form a "green" composite, which is then carbonized to formthe carbon/carbon composite. They may also comprise carbonreinforcements in which the matrix is introduced fully or in part bychemical vapor infiltration.

The carbon reinforcements are commercially available from Amoco, DuPont,Hercules, Celanese and others, and can take the form of fiber, choppedfiber, cloth or fabric, chopped cloth or fabric (referred to as mouldingcompounds), yarn, chopped yarn, and tape (unidirectional arrays offibers). Yarns may be woven in desired shapes by braiding or bymultidirectional weaving. The yarn, cloth and/or tape may be wrapped orwound around a mandrel to form a variety of shapes and reinforcementorientations. The fibers may be wrapped in the dry state or they may beimpregnated with the desired matrix precursor prior to wrapping,winding, or stacking. Such prepreg and woven structures reinforcementsare commercially available from BP Chemicals (Hitco) Inc. Thereinforcements are prepared from precursors such as polyacrylonitrile(PAN), rayon or pitch. According to a preferred embodiment of thepresent invention, the reinforcement is in the form of woven cloth.

Matrix precursors which may be used to form carbon/carbon compositesaccording to the present invention include liquid sources of high purity(that is, semiconductor quality) carbon, such as phenolic resins andpitch, and gaseous sources, including hydrocarbons such as methane,ethane, propane and the like. Representative phenolics include, but arenot limited to, phenolics sold under the trade designations USP 39 and91LD, such as supplied by Stuart Ironsides, of Willowbrook, Ill.

The carbon/carbon composites useful in the present invention may befabricated by a variety of techniques. Conventionally, resin impregnatedcarbon fibers are autoclave-or press-molded into the desired shape on atool or in a die. The molded parts are heat-treated in an inertenvironment to temperatures from about 700° C. to about 2900° C. inorder to convert the organic phases to carbon. The carbonized parts arethen densified by carbon chemical vapor impregnation or by multiplecycle reimpregnations with the resins described above. Other fabricationmethods include hot-pressing and the chemical vapor impregnation of drypreforms. Methods of fabrication of carbon/carbon composites which maybe used according to the present invention are described in U.S. Pat.No. 3,174,895 and 3,462,289, which are incorporated by reference herein.

Shaped carbon/carbon composite parts for semiconductor processingcomponents can be made either integrally before or after carbonization,or can be made of sections of material joined into the required shape,again either before or after carbonization.

Once the general shape of the carbon/carbon composite article isfabricated, the piece can be readily machined to precise tolerances, onthe order of about 0.1 mm or less. Further, because of the strength andmachinability of carbon/carbon composites, in addition to the shapingpossible in the initial fabrication process, carbon/carbon compositescan be formed into shapes for components that are not possible withgraphite.

The high purity carbon/carbon composite according to the presentinvention has the properties of conventionally produced carbon/carboncomposites, yet has improved purity resulting from the process for theproduction of a semiconductor standard composite of the presentinvention.

According to the inventive process, fiber (reinforcement) purity isenhanced by the carbon fiber reinforcement, preferably in the form ofwoven fabric, being heat treated in a non-oxidizing (inert) atmosphereto a temperature of about 2400° C. (43500 F.) to about 3000° C. toremove impurities. This heat treatment further sets the reinforcements,avoiding shrinkage in later procedures.

Carbon matrix purity is enhanced by the utilization of high puritymatrix precursors in the impregnation of the heat treated carbonreinforcement. The purity level of the carbon sources should be lessthan about 50 ppm metals. For example, the phenolic resins shouldcontain less than about 50 ppm metals, should utilize non-metallicaccelerators for cure, and preferably should be made in a stainlesssteel reactor.

The impregnated reinforcements, or prepregs, are staged, laid-up, curedand carbonized (or pyrolized) conventionally, except that processingconditions are maintained at semiconductor standards. The carbonizedpart is then densified by chemical vapor impregnation or liquid pressureimpregnation, using the carbon source materials mentioned above.

In the chemical vapor deposition (CVD) densification of the carbonizedpart, precautions are taken not to introduce any elemental impurities inthe CVD furnace. Prior to processing the carbonized parts, the furnaceis purged by running an inert gas, such as argon, helium or nitrogen,through it for several heat treat cycles at about 2400° C. to about3000° C.

After the component has been formed by the densification of thecarbonized part, the component is further heat treated at 2400° C. toabout 3000° C. in a non-oxidizing or inert atmosphere to ensuregraphitization of the structure and to remove any impurities that mayhave been introduced. The period of time for this procedure iscalculated based upon graphitization time/temperature kinetics, takinginto account furnace thermal load and mass. The component may bemachined, if desired, to precise specifications and tolerances, asdiscussed above.

In a further purification procedure, the heat treated components arefurther heat treated at 2400° C. to about 3000° C. in a halogenatmosphere to remove any remaining metallic elements as thecorresponding volatile halides. Suitable halogens include chlorine,bromine and iodine, with chlorine being preferred. The purificationtreatment may be terminated when no metallic species are detected in theoff-gas.

Throughout the production process, great care is taken not tocontaminate any parts. As discussed above, processing is done tosemiconductor standards, including the use of laminar air flow in workareas which ensure ISO 1000 conditions.

High purity carbon/carbon composites prepared according to the presentinvention were analyzed by inductively coupled plasma spectroscopy (ICP)in comparison with conventional graphite components, the latter of whichwas also analyzed by atomic absorption spectroscopy (AAS), and theresults are shown in Table I below.

                  TABLE I                                                         ______________________________________                                                               Detection                                                                              High Purity                                   Element (ppm)                                                                            Graphite (1)                                                                              Limit (2)                                                                              C/C Level (2)                                 ______________________________________                                        Aluminum   <0.08       0.1      ND                                            Calcium    0.13        0.1      ND                                            Chromium   <0.07       0.01     ND                                            Copper     <0.08       0.02     ND                                            Iron       0.09        0.04     0.18                                          Magnesium  <0.02       0.02     ND                                            Manganese  <0.08       0.01     ND                                            Nickel     <0.10       0.04     ND                                            Potassium  <0.10       4        ND                                            Sodium     <0.05       0.2      ND                                            Vanadium   <0.07       0.02      .24                                          ______________________________________                                         (1) by ICP, AAS                                                               (2) by ICP                                                                    ND -- Not Detected                                                       

High purity carbon/carbon composites prepared according to the presentinvention were analyzed by inductively coupled plasma spectroscopy incomparison with conventional carbon/carbon composites, the latter ofwhich was analyzed by high temperature halonization, and the results areshown in Table II below.

                  TABLE II                                                        ______________________________________                                                   Conventional                                                                              Detection                                                                              High Purity                                   Element (ppm)                                                                            C/C (1)     Limit (2)                                                                              C/C Level (2)                                 ______________________________________                                        Aluminum   4           0.1      ND                                            Calcium    10-30       0.1      ND                                            Chromium   <0.32       0.01     ND                                            Copper     <0.06       0.02     ND                                            Iron       3-5         0.04     0.18                                          Magnesium  3-5         0.02     ND                                            Manganese  0.034       0.01     ND                                            Molybdenum 1           0.02     ND                                            Nickel     ND          0.04     ND                                            Phosphorous                                                                              5.8         0.02     ND                                            Potassium  ND          4        ND                                            Sodium     4.8         0.2      ND                                            ______________________________________                                         (1) by High Temperature Halonization                                          (2) by Inductively Coupled Plasma Spectroscopy (ICP)                          ND = Not Detected                                                        

As shown in Tables I and II, the high purity carbon/carbon composites ofthe present invention are below the detection limit for inductivelycoupled plasma spectroscopy analysis for the metals Al, Ca, Cr, Cu, K,Mg, Mn, Mo, Na, Ni, and P, while these metal impurities are shown to bepresent in graphite, and in conventional carbon/carbon compositematerials (except in the latter, for nickel and potassium).

Carbon/carbon composites produced according to the invention were ashedand the diluted residue further analyzed by inductively coupled plasmaspectroscopy for metals content in addition to those metals testedabove. As demonstrated in Table III below, the concentration of thesemetals, Ag, Ba, Be, Cd, Co, Pb, Sr, and Zn, was also below the detectionlimit for the analytical technique.

                  TABLE III                                                       ______________________________________                                                   DETECTION LIMIT                                                                             HIGH PURITY C/C                                      ELEMENT    (PPM)         LEVEL                                                ______________________________________                                        Barium     0.01          ND                                                   Beryllium  0.01          ND                                                   Cadmium    0.01          ND                                                   Cobalt     0.02          ND                                                   Lead       0.2           ND                                                   Silver     0.02          ND                                                   Strontium  0.02          ND                                                   Zinc       0.02          ND                                                   ______________________________________                                         ND = Not Detected                                                        

Carbon/carbon composites, according to the invention, can be used insemiconductor processing without first coating the component, althoughit is preferable to precoat the carbon/carbon composite prior to use, inorder to lock down any particles which may have formed as a result ofthe composite fabrication or machining process. A coating may be desiredin the event of a change in the process furnace atmosphere.Carbon/carbon composites can readily be coated with a protectiverefractory coating, such as refractory carbides, refractory nitrides,and, particularly with regard to the production of gallium arsenidecrystals, refractory borides. Preferred refractory coatings are siliconcarbide, silicon nitride, boron nitride, pyrolytic boron nitride andsilicon boride. Graded or layered coatings of the carbides, nitrides andborides may also be used.

Advantages of carbon/carbon (C/C) composites over graphite, particularlywith regard to semiconductor processing such as in the semiconductorcrystal growing process furnace, arise from improved mechanicalproperties, namely improved strength, dimensional stability, and impactand thermal shock resistance, in part due to the incorporation of thereinforcement fibers. Representative graphite components andcarbon/carbon composite components prepared according to the presentinvention were tested for physical, thermal and mechanical properties,the results for which are reported in Table IV.

                  TABLE IV                                                        ______________________________________                                                          Graphite                                                                              C/C Composite                                       ______________________________________                                        Physical Property                                                             Density (g/cc)      1.72-1.90 1.64-1.69                                       Porosity (%)         9-12      2-15                                           Hardness (Shore)    12-80     Off Scale                                       Thermal Property                                                              Conductivity (W/mK)  70-130   100                                             TEC (×10.sup.-6 in/in/°C.)                                                           2.0-3.6   1.4 (in plane)                                                                6.3 (x-ply)                                     Emissivity          0.77      0.52                                            Mechanical Property                                                           Ultimate Tensile Strength (ksi)                                                                   0.9-1.7   35-50                                           Tensile Modulus (msi)                                                                             0.8-1.7   3.5-16                                          Flexural Strength (ksi)                                                                           1.7-13    16-42                                           Compressive Strength (ksi)                                                                        4.4-22    11-30                                           Fracture Toughness (Izod Impact ft-lb/in)                                                         <1         13                                             ______________________________________                                    

Although the properties in Table IV above were tested for compositesproduced according to a preferred embodiment of the invention, the highpurity, semiconductor standard carbon/carbon composites of the presentinvention can be produced to exhibit a density of about 1.6 to about 2g/cc, and a porosity of about 2 to about 25%. These high puritycomposites generally range in tensile strength from about 25 to about100 ksi, in tensile modulus from about 3 to about 30 msi, in flexuralstrength from about 15 to about 60 ksi, in compressive strength fromabout 10 to about 50 ksi, and in fractural toughness as measured by Izodimpact, about 5 to about 25 ft-lb/in.

Such inventive high purity composites exhibit a thermal conductivity ofabout 20 to about 500 W/mK in plane and about 5 to about 200 W/mKcross-ply, thermal expansion coefficients of zero to about 2×10⁻⁶in/in/°C. in plane and about 6×10⁻⁶ in/in/°C. to about 10×10⁻⁶ in/in/°C.cross ply. Thermal emissivity of the high purity composites is about 0.4to about 0.8. The electrical resistivity of the high purity compositesis about 1×10⁴ to about 1×10⁻² ohm-cm.

According to the present invention, the high purity, semiconductorstandard carbon/carbon composites are formed into components for use insemiconductor processing, such as furnace heat shields, furnace tubeliners, and crucible susceptors. These components are useful in theCzochralski crystal growing furnace for producing semiconductor crystalsor ingots of silicon, as well as other semiconductor materials such asgallium arsenide.

According to the invention therefore, Czochralski process furnacecomponents such as heat shields and crucible susceptors have beenfabricated, comprising a high purity, semiconductor standard compositeincluding a carbon fiber reinforced carbon matrix having a level ofmetal impurity below the detection limit of inductively coupledspectroscopy for the metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Mg,Mn, Mo, Na, Ni, P, Pb, Sr and Zn.

The high purity carbon/carbon composite susceptors have been used in theCzochralski crystal growing process for pulling a silicon ingot from asilicon melt. In this process, the silicon melt was formed in a quartzcrucible, which was intimately supported within the furnace by thesusceptor. Also, a high purity carbon/carbon composite furnace heatshield was disposed between the crucible containing the silicon melt andthe furnace heating elements.

As shown in the sectional schematic of FIGS. 1 and 1A, a typicalCzochralski semiconductor processing reactor comprises a furnace 10having a water jacketed stainless steel wall 11 to enclose theprocessing area. Insulation, not shown, protects the wall from theinternal heating elements 12. Disposed radially inwardly of the heatingelements 12 is the crystal- or ingot-pulling zone 13, where thesemiconductor material is melted and processed.

Within the crystal pulling zone 13, a crucible 14, suitably made ofquartz, is intimately supported by the high purity composite cruciblesusceptor 15 which rests either on a refractory hot surface, insulation,an axle for rotation of the crucible susceptor 15, or another furnacecomponent (not shown). The semiconductor material is heated within thecrucible 14 to form a melt 16, from which a crystal or ingot 17 is drawnby conventional crystal drawing means 18, such as a weighted pulley. Thesemiconductor material is highly pure, electronic quality silicon orgallium arsenide. The crystal pulling zone 13 may be maintained at asubatmospheric pressure, by means for evacuating the furnace (notshown).

As shown in FIG. 1, the heating elements 12 and the crystal pulling zone13 is disposed a furnace heat shield or furnace tube liner 19,comprising the high purity composite. The crucible susceptor 15, andparticularly the heat shield or tube liner 19, protect the crystalpulling zone 13 and the melt 16 and crystal 17 contained therein frompotentially contaminating elements.

These high purity composite components provide a stable thermalenvironment in which the solidification of the crystal or ingot 17 ispermitted to proceed without non-uniformity causing thermal excursions.The heat shield 19 as shown in FIG. 1, helps to maintain the crystalpulling zone 13 at an optimum temperature for the semiconductor materialbeing processed such as about 1450° C. for silicon, even though theouter surface of the shield, exposed to the heating elements 12, mayexperience a much higher temperature such as 1500° C. to 2000° C. Thecrucible susceptor 15 intimately supports the crucible 14, which maysoften and begin to "flow" at operating temperatures. The susceptor 15maintains the structural integrity of the crucible 14 during operation.

As shown in FIG. 1A, in a smaller furnace design the heat shield 19 canbe disposed radially outside of a configuration comprising a crucible 14within a susceptor 16 in close proximity to the heating elements 12 inorder to contain heat within the crystal pulling zone 13 and prevent itsdissipation radially.

The high purity composites are also resistant to thermal shock andheat/cool cycles, offering an improvement over conventional graphitecomponents. Other advantageous thermal characteristics are listed inTable IV, above.

As shown in FIGS. 2, 3 and 4, the furnace heat shield or furnace tubeliner 20 can be a generally cylindrical shape, although not beinglimited to that configuration, having a high purity composite wall 21defining an internal opening 22. The crystal pulling zone 13 can becontained within the opening 22.

As shown in FIGS. 5, 6 and 7, the crucible susceptor 30 has a highpurity composite side wall 31, a top opening 32 and a high puritycomposite base 33. The interior of the crucible susceptor 30 is shapedto hold the particular crucible design for which it was intended, andthus the base 33 can be scooped in the form of a bowl, and the side wall31 can contain a ridge 34 such as for nesting the crucible. The sidewall 31 may contain fixturing holes 35 for mounting the susceptor 30.

In an alternative embodiment shown in FIGS. 8, 9 and 10, the cruciblesusceptor 40 also has a high purity composite side wall 41, a topopening 42 and a high purity composite base 43. The base 43 may also bescooped, and the side wall 41 can contain one or more ridges 44.Fixturing holes 45 may be present in the side wall 41. The base 43 cancontain a high purity composite fitting 46 which defines an engagementzone 47 that may engage an axle for rotating the crucible/cruciblesusceptor assembly, an exhaust tubing for lowering the pressure of thefurnace interior, or another furnace component. The ease of fabricationof the high purity carbon/carbon composite materials prior tocarbonization, and their machinability after carbonization, permits thefabricating the furnace components into any desired configuration.

The following advantages have been realized using the high puritycomposite components of the present invention in the CZ crystal growingapparatus. The improved durability of the high purity carbon/carboncomposite components results in a reduction in furnace downtime. Thetypical lifetime for graphite components in the CZ semiconductor crystalgrowing industry is three to four months, while for the high puritycomposite components, a lifetime of 12 to 15 months can be realized,based on an extrapolation of real time in-situ testing.

The durability of the high purity carbon/carbon composite components isdue to their superior thermal and mechanical properties. In addition,the affinity of silicon oxides for the high purity composite material issubstantially less than that of graphite, which reduces the need forperiodic cleaning and replacement.

The improved purity of the high purity carbon/carbon compositecomponents over graphite results in a reduced level of contamination ofthe silicon ingots and wafers. This is evidenced by the time taken foran electrical current to flow between contaminating atoms (the HallMobility). The shorter the time for the current to flow between thecontaminating atoms, the more "impure" the silicon wafer is.

Electrical breakdown times for silicon wafers produced from furnacesemploying graphite and high purity carbon/carbon composite componentswere tested. Electrical breakdown times for silicon wafers produced fromfurnaces utilizing graphite components ranged from 200 to 250microseconds. The wafers produced by the high purity carbon/carboncomposite component-utilizing furnaces are considerably purer,exhibiting electrical breakdown times of greater than 300 microseconds.This improvement is highly significant to the semiconductor industry.

In another measurement of impurity concentrations in graphite and theinventive material, impurity transfer into silicon was measured bydirect contact at 550° C. over a period of 12 hours. It was determinedthat the elemental impurities listed in Tables I and II were lower inthe inventive material than in graphite by a factor of at least onehundred (100).

The use of high purity carbon/carbon composite components in the CZcrystal growing reactor results in significant improvements in the yieldof silicon wafers that are classified as "good for structure". The yieldof "good for structure" wafers produced with graphite furnace componentswas 68%, while the yield of "good for structure" wafers produced withhigh purity carbon/carbon composite furnace components was 72%. Itshould be noted that in the silicon semiconductor wafer manufacturingindustry, a 1% increase in yield is regarded as extremely financiallysignificant. This difference in good for structure yield may beattributable to the superior control of thermal conductivity throughoutthe high purity carbon/carbon composite components over time. Verylittle degradation of thermal properties of the inventive materials wereobserved.

An additional and unexpected benefit from the use of the high puritycarbon/carbon composite components over graphite concerned theproduction of large components. The fabrication of large graphite partsis difficult due to graphite's low mechanical properties and graphite'sinability to support its own weight. On the other hand large parts wereable to be made from high purity carbon/carbon composites with ease, forexample, up to 48 inches in diameter.

Regarding power consumption, the electrical power required by a CZfurnace equipped with high purity carbon/carbon composite components wassignificantly less than that of a similar furnace equipped withconventional graphite parts. This is due to the superior thermalcharacteristics of the high purity carbon/carbon composite components,as shown above. Furnaces utilizing the high purity composite furnacetube liner experienced a 2% to 5% decrease in the amount of powerrequired, depending upon the number of components in the furnace. Thispower savings is very significant, in terms of capital requirements aswell as operating costs.

Regarding particulation, high purity carbon/carbon composite componentsexhibited outstanding resistance to the generation of dust particlesrelative to conventional graphite, which is described by those skilledin the art as mealy. The contamination of silicon wafers produced infurnaces with high purity carbon/carbon composite components issubstantially lessened, as compared to those produced with graphitecomponents.

Therefore, the objects of the present invention are accomplished by theproduction and use of high purity carbon/carbon composite components foruse in semiconductor processing. The mechanical and purity advantages ofthe inventive material with respect to graphite, and the purityadvantages of the inventive material with respect to graphite andconventional carbon/carbon composites has been demonstrated, as is shownabove. It should be understood that the present invention is not limitedto the specific embodiments described above, but includes thevariations, modifications and equivalent embodiments that are defined bythe following claims.

I claim:
 1. A semiconductor crystal growing apparatus comprising atleast one high purity, carbon/carbon composite component, said highpurity composite including a carbon fiber reinforced carbon matrixhaving a level of metal impurity below the detection limit ofinductively coupled plasma spectroscopy for the metals Ag, Al, Ba, Be,Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn;wherein thecarbon fiber is selected from the group consisting of fiber, cloth,woven fabric, yarn and tape; the high purity composite having anultimate tensile strength of about 25 to about 100 ksi and a tensilemodulus of about 3 to about 30 msi, and having a flexural strength ofabout 15 to about 60 ksi and a compressive strength of about 10 to about50 ksi.
 2. The apparatus of claim 1 further comprising at least oneheating element and a crystal growing zone for drawing a semiconductorcrystal from a semiconductor material melt, wherein said high puritycomposite component is a heat shield disposed between said at least oneheating element and said crystal growing zone.
 3. The apparatus of claim1 further comprising at least one heating element and a crystal growingzone for drawing a semiconductor crystal from a semiconductor materialmelt, wherein said melt is contained in a crucible within the crystalgrowing zone and said high purity composite component is a cruciblesusceptor intimately supporting said crucible.
 4. The apparatus of claim1 further comprising at least one heating element and a crystal growingzone for drawing a semiconductor crystal from a semiconductor materialmelt, said melt contained in a crucible within the crystal growing zone,wherein at least one said high purity composite component is a heatshield disposed between said at least one heating element and saidcrystal growing zone and at least a second said high purity compositecomponent is a crucible susceptor intimately supporting said crucible.5. The apparatus of claim 1 further comprising at least one heatingelement in thermal proximity to a crystal growing zone for drawing asemiconductor crystal from a semiconductor material melt, wherein saidhigh purity composite component is a heat shield disposed radiallyoutwardly of said at least one heating element and said crystal growingzone.
 6. The apparatus of claim 1 further comprising at least oneheating element in thermal proximity to a crystal growing zone fordrawing a semiconductor crystal from a semiconductor material melt, saidmelt contained in a crucible within the crystal growing zone, wherein atleast one said high purity composite component is a heat shield disposedradially outwardly of said at least one heating element and said crystalgrowing zone and at least a second said high purity composite componentis a crucible susceptor intimately supporting said crucible.
 7. ACzochralski crystal growing process for pulling a semiconductor ingotfrom a semiconductor material melt, including:providing thesemiconductor material melt in a quartz crucible, and, intimatelysupporting the crucible with a crucible susceptor comprising a highpurity semiconductor standard composite of carbon fiber reinforcedcarbon matrix having a level of metal impurity below the detection limitof inductively coupled plasma spectroscopy for the metals Ag, Al, Ba,Be, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn; whereinthe carbon fiber is selected from the group consisting of fiber, cloth,woven fabric, yarn, and tape; the high purity composite having anultimate tensile strength of about 25 to about 100 ksi and a tensilemodulus of about 3 to about 30 msi, and having a flexural strength ofabout 15 to about 60 ksi and a compressive strength of about 10 to about50 ksi.
 8. The process of claim 7, wherein the semiconductor ingot is asilicon ingot, including cutting the silicon ingot into silicon wafers,and further including providing said silicon wafers with an electricalbreakdown time of greater than 300 microseconds.
 9. The process of claim7, wherein the semiconductor is selected from the group consisting ofsilicon and gallium arsenide.
 10. A Czochralski crystal growing processfor pulling a semiconductor ingot from a semiconductor material melt,including:providing the semiconductor material melt in a crystal pullingzone disposed in thermal contact with at least one heating element, and,disposing radially outwardly of said crystal pulling zone and said atleast one heating element, a heat shield comprising a high purity,semiconductor standard composite of carbon fiber reinforced carbonmatrix having a level of metal impurity below the detection limit ofinductively coupled plasma spectroscopy for the metals Ag, Al, Ba, Be,Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn; wherein thecarbon fiber is selected from the group consisting of fiber, cloth,woven fabric, yarn, and tape; the high purity composite having anultimate tensile strength of about 25 to about 100 ksi and a tensilemodulus of about 3 to about 30 msi, and having a flexural strength ofabout 15 to about 60 ksi and a compressive strength of about 10 to about50 ksi.
 11. The process of claim 10, wherein the semiconductor ingot isa silicon ingot, including cutting the silicon ingot into siliconwafers, and further including providing said silicon wafers with anelectrical breakdown time of greater than 300 microseconds.
 12. Theprocess of claim 10, wherein the semiconductor is selected from thegroup consisting of silicon and gallium arsenide.
 13. A Czochralskicrystal growing process for pulling a semiconductor ingot from asemiconductor material melt, including providing the semiconductormaterial melt in a quartz crucible, wherein the quartz crucible isisolated from contaminant sources by at least one high purity,carbon/carbon composite component comprising a high purity,semiconductor standard composite of carbon fiber reinforced carbonmatrix having a level of metal impurity below the detection limit ofinductively coupled plasma spectroscopy for the metals Ag, Al, Ba, Be,Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn;wherein thecarbon fiber is selected from the group consisting of fiber, cloth,woven fabric, yarn, and tape; the high purity composite having anultimate tensile strength of about 25 to about 100 ksi and a tensilemodulus of about 3 to about 30 msi, and having a flexural strength ofabout 15 to about 60 ksi and a compressive strength of about 10 to about50 ksi.
 14. The process as in claim 13, wherein the component isselected from the group consisting of crucible susceptor, furnace heatshield and furnace tube liner.
 15. The process of claim 14, wherein thesemiconductor is selected from the group consisting of silicon andgallium arsenide.
 16. The process of claim 15, wherein the componentincludes at least one said crucible susceptor and at least one of saidfurnace heat shield and said furnace tube liner.
 17. A high puritycomposite comprising a carbon fiber reinforced carbon matrix having alevel of total metal impurity less than about 5 parts per million forthe metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na,Ni, P, Pb, Sr, V and Zn;wherein the carbon fiber is selected from thegroup consisting of fiber, cloth, woven fabric, yarn, and tape; the highpurity composite having an ultimate tensile strength of about 25 toabout 100 ksi and a tensile modulus of about 3 to about 30 msi, andhaving a flexural strength of about 15 to about 60 ksi and a compressivestrength of about 10 to about 50 ksi.
 18. The high purity composite ofclaim 17 wherein the carbon fiber is woven fabric.
 19. The high puritycomposite of claim 17 wherein the carbon matrix comprises carbonizedhigh purity carbon matrix precursors, wherein the precursor containsless than about 50 ppm metals.
 20. The high purity composite of claim 19wherein the carbon matrix precursor was a gaseous hydrocarbon.
 21. Thehigh purity composite of claim 17 wherein the carbon matrix comprisescarbonized high purity phenolic resin.
 22. The high purity composite ofclaim 17 wherein the carbon matrix comprises carbonized high puritypitch.
 23. The high purity composite of claim 17 having an ultimatetensile strength of about 35 to about 50 ksi and a tensile modulus ofabout 3.5 to about 16 msi.
 24. The high purity composite of claim 17having a flexural strength of about 16 to about 42 ksi and a compressivestrength of about 11 to about 30 ksi.
 25. The high purity composite ofclaim 17 having a fracture toughness as measured by Izod impact of about5 to about 25 ft lb/in.
 26. The high purity composite of claim 17 havingan in plane thermal expansion coefficient of zero to about 2×10⁶ and across-ply thermal expansion coefficient of about 6 to about 10×10⁶. 27.The high purity composite of claim 17 having an in-plane thermalconductivity of about 20 to about 500 W/mK and a cross-ply thermalconductivity of about 5 to about 200 W/mK.
 28. The high purity compositeof claim 17 having a thermal emissivity of about 0.4 to about 0.8. 29.The high purity composite of claim 17 having a refractory coatingselected from the group consisting of carbides, nitrides, and borides.30. The high purity composite of claim 17 having a refractory coating ofsilicon carbide.
 31. The high purity composite of claim 17 having anelectrical resistivity of about 1 ×10⁻⁴ to about 1×10⁻² ohm-cm.
 32. Thehigh purity composite of claim 17 containing about 0.18 ppm iron orless.
 33. The high purity composite of claim 17 containing about 0.24ppm vanadium or less.
 34. A Czochralski process furnace componentcomprising a high purity, semiconductor standard composite comprisingthe carbon fiber reinforced carbon matrix of any of claims 17 through33.
 35. The furnace component of claim 34 selected from the groupconsisting of crucible susceptor, furnace heat shield and furnace tubeliner.
 36. A semiconductor crystal growing apparatus comprising at leastone high purity, carbon/carbon composite component, said high puritycomposite including a carbon fiber reinforced carbon matrix having alevel of total metal impurity of less than about 5 parts per million forthe metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na,Ni, P, Pb, Sr, V and Zn;wherein the carbon fiber is selected from thegroup consisting of fiber, cloth, woven fabric, yarn and tape; the highpurity composite having an ultimate tensile strength of about 25 toabout 100 ksi and a tensile modulus of about 3 to about 30 msi, andhaving a flexural strength of about 15 to about 60 ksi and a compressivestrength of about 10to about 50 ksi.
 37. The apparatus of claim 36further comprising at least one heating element and a crystal growingzone for drawing a semiconductor crystal from a semiconductor materialmelt, wherein said high purity composite component is a heat shielddisposed between said at least one heating element and said crystalgrowing zone.
 38. The apparatus of claim 36 further comprising at leastone heating element and a crystal growing zone for drawing asemiconductor crystal from a semiconductor material melt, wherein saidmelt is contained in a crucible within the crystal growing zone and saidhigh purity composite component is a crucible susceptor intimatelysupporting said crucible.
 39. The apparatus of claim 36 furthercomprising at least one heating element and a crystal growing zone fordrawing a semiconductor crystal from a semiconductor material melt, saidmelt contained in a crucible within the crystal growing zone, wherein atleast one said high purity composite component is a heat shield disposedbetween said at least one heating element and said crystal growing zoneand at least a second said high purity composite component is a cruciblesusceptor intimately supporting said crucible.
 40. The apparatus ofclaim 36 further comprising at least one heating element in thermalproximity to a crystal growing zone for drawing a semiconductor crystalfrom a semiconductor material melt, wherein said high purity compositecomponent is a heat shield disposed radially outwardly of said at leastone heating element and said crystal growing zone.
 41. The apparatus ofclaim 36 further comprising at least one heating element in thermalproximity to a crystal growing zone for drawing a semiconductor crystalfrom a semiconductor material melt, said melt contained in a cruciblewithin the crystal growing zone, wherein at least one said high puritycomposite component is a heat shield disposed radially outwardly of saidat least one heating element and said crystal growing zone and at leasta second said high purity composite component is a crucible susceptorintimately supporting said crucible.
 42. A Czochralski crystal growingprocess for pulling a semiconductor ingot from a semiconductor materialmelt, including;providing the semiconductor material melt in a quartzcrucible, and, intimately supporting the crucible with a cruciblesusceptor comprising a high purity, semiconductor standard composite ofcarbon fiber reinforced carbon matrix having a level of total metalimpurity of less than about 5 parts per million for the metals Ag, Al,Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, V andZn; wherein the carbon fiber is selected from the group consisting offiber, cloth, woven fabric, yarn, and tape; the high purity compositehaving an ultimate tensile strength of about 25 to about 100 ksi and atensile modulus of about 3 to about 30 msi, and having a flexuralstrength of about 15 to about 60 ksi and a compressive strength of about10 to about 50 ksi.
 43. The process of claim 42, wherein thesemiconductor ingot is a silicon ingot, including cutting the siliconingot into silicon wafers, and further including providing said siliconwafers with an electrical breakdown time of greater than 300microseconds.
 44. The process of claim 42, wherein the semiconductor isselected from the group consisting of silicon and gallium arsenide. 45.A Czochralski crystal growing process for pulling a semiconductor ingotfrom a semiconductor material melt, including:providing thesemiconductor material melt in a crystal pulling zone disposed inthermal contact with at least one heating element, and, disposingradially outwardly of said crystal pulling zone and said at least oneheating element, a heat shield comprising a high purity, semiconductorstandard composite of carbon fiber reinforced carbon matrix having alevel of total metal impurity of less than about 5 parts per million forthe metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na,Ni, P, Pb, Sr, V and Zn; wherein the carbon fiber is selected from thegroup consisting of fiber, cloth, woven fabric, yarn, and tape; the highpurity composite having an ultimate tensile strength of about 25 toabout 100 ksi and a tensile modulus of about 3 to about 30 msi, andhaving a flexural strength of about 15 to about 60 ksi and a compressivestrength of about 10 to about 50 ksi.
 46. The process of claim 45,wherein the semiconductor ingot is a silicon ingot, including cuttingthe silicon ingot into silicon wafers, and further including providingsaid silicon wafers with an electrical breakdown time of greater than300 microseconds.
 47. The process of claim 45, wherein the semiconductoris selected from the group consisting of silicon and gallium arsenide.48. A Czochralski crystal growing process for pulling a semiconductoringot from a semiconductor material melt, including providing thesemiconductor material melt in a quartz crucible, wherein the quartzcrucible is isolated from contaminant sources by at least one highpurity, carbon/carbon composite component comprising a high purity,semiconductor standard composite of carbon fiber reinforced carbonmatrix having a level of total metal impurity less than about 5 partsper million for the metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K,Mg, Mn, Mo, Na, Ni, P, Pb, Sr, V and Zn;wherein the carbon fiber isselected from the group consisting of fiber, cloth, woven fabric, yarn,and tape; the high purity composite having an ultimate tensile strengthof about 25 to about 100 ksi and a tensile modulus of about 3 to about30 msi, and having a flexural strength of about 15 to about 60 ksi and acompressive strength of about 10 to about 50 ksi.
 49. The process as inclaim 48, wherein the component is selected from the group consisting ofcrucible susceptor, furnace heat shield and furnace tube liner.
 50. Theprocess of claim 49, wherein the semiconductor is selected from thegroup consisting of silicon and gallium arsenide.
 51. The process ofclaim 50, wherein the component includes at least one said cruciblesusceptor and at least one of said furnace heat shield and said furnacetube liner.
 52. A Czochralski crystal growing process for pulling asemiconductor ingot from a silicon semiconductor material melt,including providing the semiconductor material melt in a quartzcrucible, wherein the quartz crucible is isolated from contaminantsources by at least one high purity, semiconductor standard compositecomponent of carbon fiber reinforced carbon matrix having a level oftotal metal impurity of less than about 5 parts per million for themetals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P,Pb, Sr, V and Zn capable of providing a yield greater than 68 percent ofgood-for-structure silicon semiconductor wafers;wherein the carbon fiberis selected from the group consisting of fiber, cloth, woven fabric,yarn, and tape; the high purity composite having an ultimate tensilestrength of about 25 to about 100 ksi and a tensile modulus of about 3to about 30 msi, and having a flexural strength of about 15 to about 60ksi and a compressive strength of about 10 to about 50 ksi.
 53. Theprocess as in claim 52, wherein the component is selected from the groupconsisting of crucible susceptor, furnace heat shield and furnace tubeliner.
 54. A Czochralski process furnace component comprising a highpurity, semiconductor standard composite comprising a high purity carbonfiber reinforced carbon matrix having a level of total metal impurity ofless than about 5 parts per million for the metals Ag, Al, Ba, Be, Ca,Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, V and Zn andexhibiting an impurity transfer of the selected metals Al, Ca, Cr, Cu,Fe, K, Mg, Mn, Mo. Na, Ni, P and V to silicon at 550° C. of less thanabout one percent the impurity transfer of said selected metals for acorresponding graphite component to silicon;wherein the carbon fiber isselected from the group consisting of fiber, cloth, woven fabric, yarn,and tape; the high purity composite having an ultimate tensile strengthof about 25 to about 100 ksi and a tensile modulus of about 3 to about30 msi, and having a flexural strength of about 15 to about 60 ksi and acompressive strength of about 10 to about 50 ksi.